The present invention relates to a chain drive, in particular camshaft/camshaft drive for an automotive engine, the chain drive comprising at least two chain gears and a drive chain.
In particular in the field of internal combustion engines, there is a need for reliably functioning control chain drives. In this respect high demands are made on the low-noise characteristics of such chain drives, so that numerous measures are taken for preventing unnecessary vibrations as well as running noise caused thereby. It is generally known that a quiet run can be expected when the number of teeth of the chain gears is great; that is why small chain gear sizes are not willingly accepted. On the other hand, more and more efforts are made to provide compact internal combustion engines as well as chain drives needed therefor. In a camshaft/camshaft drive for an automotive engine, limits are already set by the axial distance between the two camshafts, which must be kept in mind.
It is therefore the object of the present invention to improve a chain drive of the above-mentioned type with respect to its compactness, with noise or wear aspects being paid attention to.
According to the invention this object is achieved in that at least two chain gears are arranged in laterally offset relationship with one another in axial direction, the drive chain is a multiple-track chain, each of the offset chain gears has assigned thereto a separate track of the multiple-track chain due to the lateral offset, and the tip diameters of the offset toothed wheels are overlapping. Normally, multiple-track chains are only used in fields where they are in engagement with a multiple-track chain gear to be able to transmit large forces. In this case, however, a multiple-track chain is used for simultaneously driving chain gears that are laterally offset to one another, namely in the form that the chain gears are even overlapping. With a standard arrangement without a lateral offset, such an overlap would of course not be possible. At the same time, however, the number of teeth of the chain gears can be kept large despite the axial distance which is per se too small so as to achieve a run of the multiple-track chain that is as quiet as possible. Theoretically, it would be possible with such an arrangement to make the chain gears overlapping to such an extent that the gearing of the one chain gear almost contacts the axis of the other chain gear. When a projection of the axes is avoided, an even greater overlap would be possible. However, the two chain gears should not be seated on a joint axle or shaft, but should drive different elements (e.g. camshafts). The number of the offset chain gears can be chosen in dependence upon the number of the tracks of the multiple-track chain. The chain gears can have different tooth numbers.
In dependence upon the speeds to be used and the forces to be transmitted, it may further be necessary for the prevention of tilting moments that at the side next to the gearings of the overlapping chain gears a respective support means is provided for the track of the multiple-track chain that is not in engagement with the associated chain gear. The force of the chain gear acting on the multiple-track chain is asymmetrical relative to the longitudinal center line of the multiple-track chain, so that corresponding asymmetrical forces are acting thereon. Support means help to prevent a lateral tilting of the multiple-track chain, whereby noise can once again be minimized because corresponding vibrations are suppressed.
Track means each time that part of the multiple-track chain that is laterally provided next to a chain gear but not in engagement therewith. Said track is of course in engagement with the respectively other chain gear.
In case the track is to be supported by the chain gears themselves, such a configuration has its limits. It is therefore preferred in one embodiment that an overlap of the chain gears is greater than the sum of the height of the plates of the multiple-track chain and of the difference of tip circle radius less pitch circle radius. A support means integrated on the chain gear would come into contact with the gearing of the respectively other chain gear in the case of such a dimensioning rule.
According to a further embodiment it is therefore intended to provide slide rails as support means. As a rule, these are at a standstill relative to the chain gears, and the track is sliding therealong. Slide rails have already been used in chain drives for very different purposes for a long time so that the problems associated therewith have already been solved in the prior art in many ways. Materials and, if necessary, also lubricant supply can readily be used for the slide rails. It is also possible to choose a multipart construction of the slide rails. Known is e.g. the use of a relatively stable basic body and a slide lining which is arranged thereon and can be removed and exchanged in part.
Preferably, a distance of the slide surface of the slide rail may substantially be equal to half the plate height or half a roller height at least in the area of the wrap angle of the multiple chain on the associated chain gear to the pitch circle of the chain gear. It is here of importance whether the plates are to be supported by the support means or whether the rollers of a multiple-track chain are to be used for the support. The dimensioning rule ensures that the hinge axes of the multiple-track chains are oriented as parallel as possible relative to the axes of the chain gears.
According to a further variant a great advantage is that the slide rail comprises a transfer extension which supports the track of the multiple-track chain in the section between the overlapping chain gears. Despite the overlapping chain gears a section remains in most cases between the two wheels where the multiple-track chain is neither in engagement with the one nor the other chain gear. To avoid excessive vibrations and associated noise upon exit from the one chain gear and/or entry on the other chain gear, a support is also provided for this area.
Advantageously, the transfer extensions of the slide rails assigned to the overlapping chain gears can overlap and jointly support the multiple-track chain in the section between the overlapping chain gears. When both slide rails are equipped with such transfer extensions, a tilting movement of the multiple-track chain is also avoided in the intermediate part between the chain gears because the multiple-track chain is supported over its whole width.
A smooth entry or exit of the multiple-track chain is ensured when according to one embodiment a slide surface of the transfer extension passes tangentially into the adjoining remaining slide surface of the slide rail.
To give the slide rail a sufficiently stable configuration and to make the transfer extension as rigid as possible, a bottom side of the slide rail which defines at least the transfer extension is arcuately adapted to the outer contour of the other chain gear. In a particular embodiment this has even the effect that the multiple-track chain is completely supported between the exit point on the first chain gear and the exit point from the second one of the overlapping chain gears. The transfer extensions are guided relatively close to the other chain gear, resulting each time in only small portions on which the track is not supported. However, the multiple-track chain is respectively supported in said portions by the transfer extensions arranged in offset configuration relative thereto. The bottom side of the transfer extension is each time adapted relatively close to the outer contour of the adjoining chain gear, so that a stable support of the slide surface can be realized without a design that is too filigree.
Furthermore, it is of advantage when the chain gears have the same size and tooth number. It is here in particular possible to give also the slide rails an identical design and to arrange each in offset relationship with respect to one another.